general-settings.php

<?php

class NYO_General_Settings {
    private static $_instance;

    private $option_defaults = array(
        'trending_title' => array(
            'sanitizer' => 'sanitize_text_field',
            'default' => 'Trending:',
        )
    );

    private function __construct() {
        add_action( 'admin_menu', array( $this, 'action_admin_menu' ) );
        add_action( 'admin_init', array( $this, 'action_admin_init' ) );
    }

    public static function get_instance() {
        if ( empty( self::$_instance ) ) {
            self::$_instance = new NYO_General_Settings();
        }

        return self::$_instance;
    }

    /**
     * Add options page
     *
     * @return void
     */
    public function action_admin_menu() {
        add_submenu_page( 'themes.php', 'Theme Settings', 'Theme Settings', 'manage_options', 'nyo-theme-settings', array( $this, 'screen_options' ) );
    }


    /**
     * Register setting and sanitization callback
     *
     * @return void
     */
    public function action_admin_init() {
        register_setting( 'nyo_general_settings', 'nyo_general_settings', array( $this, 'sanitize_options' ) );
    }

    /**
     * Sanitize options
     *
     * @param array $options
     * @return array
     */
    public function sanitize_options( $options ) {

        $new_options = array();

        foreach ( $this->option_defaults as $option_name => $option_array ) {
            if ( ! isset( $options[$option_name] ) ) {
                $value = $option_array['default'];
            } else {
                $value = $options[$option_name];
            }

            $new_options[$option_name] = call_user_func( $option_array['sanitizer'], $value );
        }

        return $new_options;
    }

    /**
     * Output settings
     *
     * @return void
     */
    public function screen_options() {
        $option = get_option( 'nyo_general_settings' );
        ?>
        <div class="wrap">
            <h2>Observer Theme Settings</h2>

            <form action="options.php" method="post">
                <?php settings_fields( 'nyo_general_settings' ); ?>
                <table class="form-table">
                    <tbody>
                        <tr>
                            <th scope="row"><label for="nyo_trending_title">Trending Title:</label></th>
                            <td>
                                <input type="text" id="nyo_trending_title" value="<?php echo esc_attr( $option['trending_title'] ); ?>" name="nyo_general_settings[trending_title]" />
                            </td>
                        </tr>
                    </tbody>
                </table>

                <?php submit_button(); ?>
            </form>
        </div>
    <?php
    }
}

NYO_General_Settings::get_instance();

/**
 * Output escaped trending title
 */
function nyo_get_trending_title() {
    $option = get_option( 'nyo_general_settings' );
    if ( ! empty( $option['trending_title'] ) ) {
        return esc_html( $option['trending_title'] );
    }

    return '';
}